As technologies of reducing the amount of nitrogen oxides (which will be hereinafter referred to as “NOx”) emitted to the atmosphere from an internal combustion engine, exhaust gas purification systems equipped with an exhaust gas recirculation apparatus (which will be hereinafter referred to as an “EGR apparatus”) or an exhaust gas purification apparatus such as NOx catalyst or a particulate filter (which will be hereinafter referred to as a “filter”) on which an NOx catalyst is supported are known.
The NOx catalyst stores NOx in the exhaust gas discharged from an internal combustion engine into it to thereby purify the exhaust gas.
The EGR apparatus is an apparatus that returns a portion of the exhaust gas to the air intake system of the internal combustion engine to reduce the combustion temperature of the air-fuel mixture in the combustion chamber thereby reducing the amount of NOx generated in the internal combustion engine.
Japanese Patent Application Laid-Open No. 2004-150319 discloses an internal combustion engine that has a turbocharger as a supercharger and is equipped with a low pressure EGR apparatus that recirculates a portion of the exhaust gas emitted from an NOx catalyst provided downstream of the turbine of the turbocharger to the intake pipe upstream of the compressor of the turbocharger in addition to a normal EGR apparatus (which will be hereinafter referred to as a “high pressure EGR apparatus”) that recirculate a portion of the exhaust gas in the exhaust pipe upstream of the turbine of the turbocharger to the intake pipe downstream of the compressor of the turbocharger.
Furthermore, Japanese Patent Application Laid-Open No. 2005-76456 discloses an internal combustion engine equipped with a high pressure EGR apparatus and a low pressure EGR apparatus in which when low-temperature combustion is performed in the internal combustion engine, the amount of the exhaust gas recirculated by the high pressure EGR apparatus and the amount of the exhaust gas recirculated by the low pressure EGR apparatus are regulated based on the required engine load.
Still further, Japanese Patent Application Laid-Open No. 2004-156572 discloses an EGR apparatus having a high pressure EGR apparatus and a low pressure EGR apparatus in which the amount of the exhaust gas recirculated by the high pressure EGR apparatus and the amount of the exhaust gas recirculated by the low pressure EGR apparatus are varied according to the operation condition of the internal combustion engine.